(1) Field of the Invention
The present invention relates to a switching system, a subscriber apparatus and a switching apparatus suitable for allowing a signaling channel for controlling setting of a virtual connection (for setup) between a switching apparatus and a subscriber apparatus to be redundant.
(2) Description of the Related Art
FIG. 19 is a block diagram showing an example of an ATM (Asynchronous Transfer Mode) switching system. The ATM switching system shown in FIG. 19 includes an ATM switch 100 having interface apparatus (OC3cs: Optical Carrier 3 concatenated) 101A through 101C, middle-speed interface multiplexing apparatus (MIFSHS: Middle Interface Shelf) 102A and 102B, an ATM switch unit (CRSWSH: Cell Relay Switch Shelf) 103, a central control apparatus (CC: Central Controller) 104, a main storage apparatus (MM: Main Memory) 105, a hard disk (Hard Disk Unit) 106, signaling control apparatus (BSGCS: Broadband Signaling Controllers) 107A and 107B and inter-processor control apparatus (PACs: Processor Access Controllers) 108, and a subscriber apparatus [line concentrator: HDT (Head-end Distribution Terminal)] 200 accommodating subscriber terminals (users) to provide VOD (Video On Demand) service and the like to the users.
Each of the above interface apparatus (OC3cs) 101A through 101C is an optical interface of a transmission capacity of about 155 Mb/s used in SONET (Synchronous Optical Network) conforming to SDH (Synchronous Digital Hierarchy) transmission system. If a transmission rate of video image in the above VOD service is 3.4 Mb/s using a desired moving picture compressing technique such as MPEG 2 or the like, each of the interface apparatus 101A and 101B can set a maximum of about 50 lines (channels) between the HDT 200 and itself.
Each of the middle-speed interface multiplexing apparatus (MIFSHS) 102A and 102B accommodates an appropriate number of interface apparatus of 155 Mb/s 101A through 101C, and multiplexes data (ATM cells) from each of the interface apparatus 101A through 101C in order to unify a data transmission rate to 2.4 Gb/s between the ATM switch unit 103 and itself.
The ATM switch unit 103 performs a self-routing process on the basis of tag information [an apparatus address, VPI (Virtual Path Identifier)/VCI (Virtual Channel Identifier) and the like to be described later] attached to a header of a received ATM cell to output the received cell to a relevant port.
The central control apparatus (CC) 104 collectively controls operations of the ATM switch 100 (call control such as setup, disconnecting and the like, accounting control, call history management, and the like). The central control apparatus (CC) 104 can suitably give necessary settings to the middle speed interface multiplexing apparatus (MIFSHS) 102A and 102B, and the ATM switch unit 103 through the above inter-processor control apparatus (PACs) 108, and the signaling control apparatus (BSGCS) 107A and 107B.
The main storage apparatus (MM) 105 stores software required in the operations of the central control apparatus 104 along with various data such as subscriber data, accounting data, history data and the like. The hard disk 106 backups contents stored in the main storage apparatus 105, or stores accounting data or history data of all subscribers that the main storage apparatus cannot manage.
In the switching system with the above structure, when a certain subscriber terminal (user) A requests for a communication with another subscriber terminal (user) B, for example, the request is transmitted to, for example, the interface apparatus 101A as a SETUP signal of an ATM cell through the HDT 200.
The interface apparatus 101A refers to a correspondence table 111 as shown in FIG. 20 managed by the interface apparatus 101A with a virtual connection number [VPI (Virtual Path Identifier)/VCI (Virtual Channel Identifier)=0/5 of the SETUP signal] attached to the header of the received ATM cell as a key to obtain an apparatus address and a signaling channel number of an opposite signaling control apparatus 107A.
The obtained apparatus address and signaling channel number are attached to the received ATM cell, and sent to the ATM switch unit 103 through the middle-speed interface multiplexing apparatus 102A.
The ATM switch unit 103 allows self-routing of the received ATM cell on the basis of the apparatus address attached to the received ATM cell, and sends out the received ATM cell to the signaling control apparatus 107A from a relevant port.
The signaling control apparatus 107A converts the received ATM cell into a signaling message form, while giving a corresponding signaling channel number to the received SETUP signal by referring to a correspondence table 112 as shown in FIG. 21 with the above apparatus address as a key and transmitting the SETUP signal to the central control apparatus 104.
The central control apparatus 104 performs processes described in {circle around (1)} through {circle around (5)} below on the basis of information in the SETUP signal received from the signaling control apparatus 107A.
{circle around (1)} referring to signaling channel management data 113 as shown in FIG. 22 with the signaling channel number attached to the received SETUP signal as a key to call corresponding physical interface management data 114, further determining a physical interface number (a number of the interface apparatus 101A) and a VPI value that should be set as a virtual communication path for a source (HDT 200) from VPCI (Virtual Path Connection Identifier) that is designated in the SETUP signal;
{circle around (2)} selecting an idle VCI in the determined VPI and determining it;
{circle around (3)} referring to subscriber number translation data 115 shown in FIG. 22 with a destination number set in the SETUP signal as a key to call corresponding subscriber data 116, obtaining a subscriber address of the destination;
{circle around (4)} calling the physical interface management data 114 corresponding (linked by a pointer) to the subscriber data 116 at the subscriber address, and determining a physical interface number (a number of the interface apparatus 101B), a VPI value and a VCI value of a virtual communication path set for the destination subscriber; and
{circle around (5)} transmitting a SETUP signal, to which a signaling channel number is attached, to the signaling control apparatus 107B accommodating a signaling channel of the destination.
The above data 113 through 116 are stored as data in a table form in the main storage apparatus 105.
When receiving the SETUP signal from the central control apparatus 104, the signaling control apparatus 107B assembles the SETUP signal into an ATM cell, while referring to a correspondence table 112 similar to that shown in FIG. 21 with the signaling channel number attached to the SETUP signal as a key to obtain an apparatus address of the opposite interface apparatus 101C, assembling the apparatus address and attaching it to the ATM cell, and sending the ATM cell to the ATM switch unit 103.
The ATM switch unit 103 transmits the received ATM cell to the interface apparatus 101C on the basis of the apparatus address attached to the received ATM cell. The interface apparatus 101C refers to a correspondence table 111 similar to that shown in FIG. 20 with the apparatus address attached to the received ATM cell as a key to obtain a virtual connection number (VPI/VCI value), sets the number to the received ATM cell, and sends out the ATM cell as a SETUP signal to the destination.
After that, signaling messages such as confirmation (SETUP ACKNOWLEDGE) of the above SETUP signal and the like are exchanged among the source, the destination and the ATM switch 100. The ATM switch 100 (central control apparatus 104) sets (notifies) the apparatus address and VPI/VCI of the opposite apparatus to each of the interface apparatus 101A and 101C on the communication route between the source and the destination determined in the above processes {circle around (1)} through {circle around (5)}, whereby a mutual communication by the ATM cell through the virtual communication route becomes possible, thus a communication between the source and the destination is possible. Incidentally, a route (path) indicated by dot-dash line represents a set route for a signaling channel, whereas a route (path) indicated by broken line represents an actual communication route (virtual connection).
Heretofore, only one signaling channel 301 for transmitting signaling messages is allocated to a physical interface 300 between the ATM switch 100 and the subscriber apparatus 200, through which the signaling messages having VPCI are exchanged between the subscriber apparatus 200 and the ATM switch 100 over the signaling channel 301, as schematically shown in FIG. 23. Whereby, VPI/VCI that should be set on the side of the ATM switch 100 is calculated from VPCI, and VC (information channel) of VP 302 or 303 corresponding to the VPI/VCI is set (acquired) as a virtual connection.
In the above known switching system, only one signaling channel 301 is allocated between the ATM switch 100 and the subscriber apparatus 200 (physical interface 300), as above. Therefore, when the signaling channel 301 is unusable due to a trouble or the like, the setup control is impossible so that a communication with the subscriber apparatus 200 [SVC (Switched Virtual Channel) communication] is impossible.
In the case where only one signaling channel is allocated to the physical interface 300 as above, a load on the signaling channel is largely increased between the ATM switch and a subscriber apparatus such as a large-capacity server on which accesses are concentrated so that it takes a very long time until the communication is commenced.
Paying attention to that a plurality of signaling channels can be defined, there is a technique called virtual UNI (User Network Interface). In this technique, a range being able to control allocation of VPCI to each signaling channel is independent to each other so that it is impossible to backup by using another signaling channel at the time of a trouble or the like on a signaling channel. It is also impossible to distribute a load on a signaling channel at the time of control of setting a virtual communication route to a subscriber apparatus over each of the above signaling channels.
In view of backup, there is APS (Automatic Protection Switching) technique in a technique of multiplexing transmission route such as SDH/SONET and the like. This is, as schematically shown in FIG. 24, for example, that a switching control apparatus 400 is disposed between the ATM switch 100 and the subscriber apparatus 200 to switch an interface in service to another (standby) physical interface 300B by the switching control apparatus 400 when the (current) physical interface 300A becomes unusable due to a trouble. The switching control apparatus 400 may be included in the subscriber apparatus 200.
However, APS technique is feasible in only a transmission system having a specific transmission format such as SDH/SONET and the like, and is very costly since it is necessary to prepare transmission apparatus (physical interfaces 300A and 300B) for the current (work) and standby (protection).
In the light of the above problems, the present invention provides a switching system, and a subscriber apparatus and a switching apparatus, in which a control of setting a virtual connection to a virtual path can be done over arbitrary plural signaling channels, whereby it is possible to backup when a signaling channel becomes unusable, or distribute a load of the control of setting a virtual communication route by simultaneously using a plurality of signaling channels.
The present invention therefore provides a switching system having a subscriber apparatus accommodating subscriber terminals and a switching apparatus accommodating the subscriber apparatus via one or more physical interface(s) to allocate a plurality of virtual paths to which virtual connections may be set to the physical interface(s) to virtually-handle the physical interface(s) as one single virtual interface, the switching system comprising the switching apparatus comprising a plural-signaling-channel setting unit for setting a plurality of signaling channels for virtual connection setting control to the virtual interface, a signaling channel information storing unit for storing signaling channel information on the plural signaling channels, a virtual interface information storing unit for storing virtual interface information for uniquely identifying a virtual path to which the virtual connection should be set in the virtual interface as information in common to the signaling channel information, a virtual connection setting control unit for identifying at least a virtual path that is an object of virtual connection setting on the basis of the virtual interface information when receiving a set request for the virtual connection from the subscriber apparatus over an arbitrary signaling channel, and setting the virtual connection to the virtual path using the signaling channel over which the set request is received, the subscriber apparatus comprising a virtual interface control unit for making a set request for the virtual connection of the switching apparatus over an arbitrary signaling channel, and a connecting process unit for performing a connecting process between the virtual path to which the virtual connection is set by the switching apparatus and the subscriber terminal.
The present invention further provides a switching system comprising a subscriber apparatus accommodating subscriber terminals and a switching apparatus accommodating the subscriber apparatus via one or more physical interface(s) to allocate a plurality of virtual paths to which virtual connections may be set to the physical interface(s) to virtually-handle the physical interface(s) as one single virtual interface, the switching system characterized by that a plurality of signaling channels for virtual connection setting control are set to the virtual interface, and the virtual connection is set to an arbitrary virtual path in the virtual interface over an arbitrary signaling channel.
According to the switching system of this invention, a plurality of signaling channels for virtual connection setting control are set to the virtual interface between a subscriber apparatus and the switching apparatus, whereby control of setting the virtual connection to an arbitrary virtual path in the virtual interface is done using an arbitrary signaling channel. It is therefore possible to allow the signaling channels to be redundant, or distribute a load on signaling channels, which leads to an improvement of reliability of a connecting service (virtual connection setting control), or decrease of delay time.
The above virtual interface information storing unit of the switching apparatus may set different identification information to each virtual connection that may be set in the virtual interface, and store identification information on the physical interface and identification information on the virtual path correspondingly to the identification information. In this case, the virtual connection setting control unit of the switching apparatus identifies a physical interface and a virtual path to which a virtual connection should be set on the basis of the identification information on the virtual connection required to be set.
The switching apparatus can thereby uniquely identify a physical interface and a virtual path to which a virtual connection should be set in the virtual interface so as to certainly set a virtual connection to a desired virtual path in the virtual interface even if receiving a set request over any signaling channel.
A predetermined order of priority may be set to the above plural signaling channels, and the virtual interface control unit of the subscriber apparatus and the virtual connection setting control unit of the switching apparatus may select a signaling channel to be used according to the order of priority.
It is thereby possible to allocate a signaling channel that is of a lower priority and hardly to be selected as a backup, so that the signaling channel is redundant quite easily and reliability of the connecting service is largely improved.
Alternatively, an identical priority may be set to the plural signaling channels, and the virtual interface control unit of the subscriber apparatus and the virtual connection setting control unit of the switching apparatus may arbitrarily select and use the plural signaling channels.
It is thereby possible to control setting of different virtual connections using different signaling channels. Accordingly, a load on each signaling channel may be distributed, thus a connecting service with less delay may be provided.
The present invention still further provides a subscriber apparatus accommodating subscriber terminals while being accommodated by a switching apparatus via one or more physical interface(s) to allocate a plurality of virtual paths to which virtual connections may be set to the physical interfaces to virtually-handle the physical interface(s) as one single virtual interface, the subscriber apparatus characterized by that a plurality of signaling channels for virtual connection setting control in the virtual interface are allocated to the virtual interface, and that the subscriber apparatus comprising a virtual interface control unit for making a set request for a virtual connection of the switching apparatus using an arbitrary signaling channel in the virtual interface, and a connecting process unit for performing a connecting process between a virtual path to which the virtual connection is set by the switching apparatus and the subscriber terminal.
According to this invention, the subscriber apparatus may make a request for setting a virtual connection of the switching apparatus using an arbitrary signaling channel in the virtual interface, while performing a connecting process between a virtual path to which a virtual connection is set by the switching apparatus and the subscriber terminal. It is therefore possible to allow a signaling channel between the subscriber apparatus and the switching apparatus to be redundant and distribute a load on the signaling channel, certainly.
In the above subscriber apparatus, a predetermined order of priority may be set to the plural signaling channels, and select signaling channels to be used according to the order of priority. In this case, a signaling channel that is not selected may be used as a backup. Accordingly, it is possible to make a signaling channel to be redundant, thus largely improve reliability of the connecting service.
Alternatively, an identical priority may be set to the plural signaling channels, and plural signaling channels may be arbitrarily selected to be used, whereby a request for setting different virtual connections are made using different signaling channels. In this case, it is also possible to readily distribute a load on the signaling channel, and provide a connecting service with less delay.
At this time, different call identification information may be set to each of the set requests to be transmitted to the switching apparatus over the plural signaling channels. In this case, it is possible to avoid a phenomenon that set requests having an identical call identification information in the virtual interface are transmitted to the switching so that setting of virtual connections is infeasible. Accordingly, distribution of a load on each signaling channel is certainly realized.
The present invention still further provides a switching apparatus accommodating a subscriber apparatus via one or more physical interface(s) to allocate a plurality of virtual paths to which virtual connections may be set to the physical interface(s) to virtually-handle the physical interface(s) as one single virtual interface, the switching apparatus comprising a plural-signaling-channel setting unit for setting a plurality of signaling channels for virtual connection setting control to the virtual interface, a signaling channel information storing unit for storing signaling channel information on the plural signaling channels, a virtual interface information storing unit for storing virtual interface information for uniquely identifying a virtual path to which the virtual connection should be set in the virtual interface as information in common to the signaling channel information, and a virtual connection setting control unit for identifying a virtual path that is an object of virtual connection setting on the basis of the virtual interface information when receiving a set request for the virtual connection from the subscriber apparatus over an arbitrary signaling channel, and setting the virtual connection to the virtual path using the signaling channel over which the set request was received.
According to the switching apparatus of this invention, a plurality of signaling channels for virtual connection setting control are set to the virtual interface, and the control of setting a virtual connection to an arbitrary virtual path is conducted using an arbitrary signaling channel. It is therefore possible to allow the signaling channel between the switching apparatus and the subscriber apparatus to be redundant and distribute a load on the same, certainly.
The above virtual interface information storing unit may set different identification information to each virtual connection that may be set in the virtual interface and store identification information on the physical interface and identification information on the virtual path correspondingly to the identification information. In this case, the virtual connection setting control unit identifies a physical interface and a virtual path to which a virtual connection should be set on the basis of the identification information on the virtual connection required to be set.
The switching apparatus of this invention can thereby uniquely identify a physical interface and a virtual path to which a virtual connection should be set in the virtual interface on the basis of the identification information on the virtual connection required to be set. Accordingly, a virtual connection may be certainly set to a desired virtual path in the virtual interface even if a set request is received over any signaling channel.
The switching apparatus of this invention may further have an attribute information storing unit for storing attribute information relating to a control on the signaling channels, thereby controlling a mode of use of the signaling channels on the basis of the attribute information in the attribute information storing unit. It is thereby possible to simply define a mode of use of the signaling channels according to a setting of the attribute information to set attribute of an operation of the switching apparatus. This largely improves flexibility of modes of the connecting service, or contributes to a decrease of a load of setting in a maintenance operation.
Alternatively, attribute information for using the plural signaling channels as a current channel and a standby channel may be set to the attribute information storing unit. In this case, according to the attribute information, the virtual connection setting control unit uses the current channel in a normal state, while switching a signaling channel in use to the standby channel to use the standby channel in an emergency where a trouble occurs in the current channel and the current channel becomes unusable.
The switching apparatus uses the current channel in a normal state, while switching a signaling channel in use to the standby channel at an emergency where a trouble occurs in the current channel and the current channel becomes unusable, so that the connecting service is not unavailable for a long time, leading to a remarkable improvement of reliability of the connecting service.
Further, attribute information about whether a signaling channel in use is switched to the current channel when a trouble occurring in the current channel is recovered and the current channel becomes usable may be set to the attribute information storing unit. In this case, if the attribute information signifying that a signaling channel in use is switched is stored in the attribute information storing unit, the virtual connecting setting control unit switches the signal channel in use to the current signaling channel after recovery of the trouble, while not switching the signaling channel in use but continuously using the standby channel if attribute information signifying that the signaling channel in use is not switched is stored in the attribute information storing unit.
The switching apparatus according to this invention switches a signaling channel in use to the current channel after recovery of a trouble if attribute information signifying that the signaling channel in use is switched is set in the attribute information storing unit, that is, uses the current channel as long as the current channel is usable. This facilitates management of the signaling channel in use. On the other hand, if attribute information signifying that a signaling channel in use is not switched is set, the switching apparatus continuously uses the standby channel even after recovery of the trouble. This can avoid a condition in which the signaling channel in use is frequently switched due to repetitive occurrence/recovery of troubles within a short period, which stabilizes the connecting service.
Still further, attribute information about whether a virtual connection having been set is relieved at the time of the signaling channel switching may be stored in the attribute information storing unit. In this case, if attribute information signifying that a virtual connection is relieved is set in the attribute information storing unit, the virtual connection setting control unit continuously controls a virtual connection in communication over a signaling channel after the switching, while initializing a virtual connection setting control on all virtual paths over the signaling channel after the switching if attribute information signifying that the virtual connection is not relieved is stored in the attribute information storing unit.
If attribute information signifying that a virtual connection having been set is relieved is set in the attribute information storing unit, the switching apparatus according to this invention continuously controls a virtual connection in communication over a signaling channel after the switching, so as to avoid a condition in which disconnecting of communication cannot done normally. On the other hand, if attribute information signifying that a virtual connection is not relieved is set in the attribute information storing unit, the switching apparatus initializes virtual connection setting control on all virtual paths over a signaling channel after the switching, so as to dissolve condition non-coincidence in the setting control that possibly occurs between the switching apparatus and the subscriber apparatus during the switching of a signaling channel within a short period.
Alternatively, attribute information for selecting a plurality of arbitrary signaling channels among the plural signaling channels to use them may be set in the attribute information storing unit. In this case, the virtual connection setting control unit selects arbitrary plural signaling channels on the basis of the attribute information and controls setting of different virtual connections over the selected signaling channels.
If attribute information for selecting arbitrary signaling channels to use them is stored in the attribute information storing unit, the switching apparatus according to this invention selects arbitrary signaling channels, and controls setting of different virtual connections over the selected signaling channels. Therefore, a load on a signaling channel is distributed so that the connecting service is be done very quickly and a connecting service with less delay is provided.
Still further, attribute information about whether a backup control is conducted on a virtual connection having been set when a trouble occurs in a part of the plural signaling channels and a relevant signaling channel becomes unusable may be set in the attribute information storing unit. In this case, if attribute information signifying that the backup control is conducted is set in the attribute information storing unit, the virtual connection setting control unit uses a signaling channel other than the part of the signaling channels to control the virtual connection having been set.
If attribute information signifying that a backup control is conducted on the virtual connection having been set when a part of the plural signaling channels becomes unusable is set in the attribute information storing unit, the switching apparatus according to this invention uses a signaling channel other than the part of the signaling channels to control the virtual connection having been set, thereby backing up a channel in which a trouble occurs while distributing a load on a signaling channel, which leads to a decrease of a delay time in the connecting service and a large improvement of the reliability.
Still further, attribute information about whether the virtual connection having been set is relieved at the time of the backup control may be set in the attribute information storing unit. In this case, if attribute information signifying that a virtual connection is relieved is set in the attribute information storing unit, the virtual connection setting control unit continues a control on a virtual connection in communication over another signaling channel to conduct the backup control.
If attribute information signifying that the virtual connection having been set is relieved at the time of the backup control is set in the attribute information storing unit, the switching apparatus according to this invention continues a control on a virtual connection in communication over another signaling channel to conduct the backup control. In this case, it is possible to avoid a condition in which disconnecting of a communication cannot be normally done.
The virtual connection setting control unit may use a plurality of arbitrary signaling channels to control setting of virtual connections in response to set requests having different call identification information.
The switching apparatus according to this invention controls setting of virtual connections in response to set requests having different call identification information, using arbitrary signaling channels. It is therefore possible to avoid a phenomenon that the switching apparatus accepts set requests having identical call identification information in the virtual interface, thus cannot set virtual connections since the switching apparatus cannot identify the set requests, and to realize distribution of a load on the signaling channel.
The switching apparatus according to this invention may further have an attribute information altering unit for altering setting of the attribute information in the attribute information storing unit according to an attribute information alter signal from a maintenance terminal for the switching apparatus.
When receiving an attribute information alter signal from the maintenance terminal, the switching apparatus according to this invention may alter setting of the attribute information in the attribute information storing unit. This largely improves versatility of the switching apparatus and flexibility of the provided connecting service.
The present invention still further provides a switching apparatus connected to a subscriber apparatus accommodating subscriber terminals via a plurality of physical lines to accept a request for set from the subscriber terminal over a signaling channel of the physical lines and acquiring an information channel of the physical lines in response to the request for set, the switching system characterized by that the switching apparatus acquires an information channel of a physical line different from a physical line to which a signaling channel over which the request for set is transmitted belongs as an information channel in response to the request for set.
The switching apparatus according to this invention can continue a control on an acquired information channel even if a signaling channel of a physical line to which the acquired information channel becomes unusable, so that reliability of the connecting service is largely improved.